Vascular bypass grafts have become important in the treatment of arterial obstructions, particularly for vessels in the heart and legs. If is well documented that hemodynamic factors influence the growth and adaptation of the arterial wall. In particular, these factors can accelerate or inhibit the excessive growth of vascular will (intimal thickening) and which can result in occlusive failure of the graft. Wall shear stress has long been considered an important variable in intimal thickening, but is only on of numerous contributing factors. The adhesion of platelets to the vessel wall and subsequent release of platelet-derived growth factor is also a necessary step for thrombosis, which can cause the final rapid occlusion of the graft opening. The path history of a platelet is important since these final rapid occlusion of the graft opening. The path history of a platelet is important since these cells can become activated by hemodynamic forces in one location and adhere in a different location. The proposed research will use numerical flow computations and particle tracing methods to determine the wall shear stress and the particle trajectories of platelets within an end-to-side anastomotic bypass graft. The results will be used to predict the growth of the vessel according to theoretical models derived from existing literature. To take this process to the point where the vessel occludes, the model must be altered and the flow field must be re-calculated for the altered geometry. This will demonstrate the feasibility of a much larger project in which models of the adaptive process are used to predict the evolution of the vessel wall over time. Once developed, it will be possible to use the technique to test specific biological models and to design appropriate graft geometries for patients with occlusive disease.